The application of general principles of morality to definite and concrete cases of human activity, for the purpose, primarily, of determining what one ought to do, or ought not to do, or what one may do or leave undone as one pleases; and for the purpose, secondarily, of deciding whether and to what extent guilt or immunity from guilt follows on an action already posited.

Being merely a science of application, casuistry must be based on the principles and established conclusions of moral theology and ethics. These normative sciences it presupposes; to them it is ancillary; and strictly speaking it is distinct from them. It does not define objective morality, nor the objective circumstances that modify morality, nor the psychological conditions that fix motive and consent; but, borrowing from the moralist the principles that determine these elements of a volitional act, its inquiry regards the extent of their presence or absence in a given case. Neither does it establish the existence of moral obligation; but, assuming the precepts of morality as already established, its only office is to determine the subjective morality of an individual act. In subordination to the sciences which it subserves, its sphere comprises the whole range of man's free activity. The decisions of the casuist are right or wrong, therefore, in so far as they are or are not in accord with a science of morality, which is itself a right interpretation of the natural or positive laws promulgated by the Supreme Legislator of the Universe. They are of no worth, when based on an arbitrary or purely self-sanctioned autonomous philosophy of conduct.

Since the special function of casuistry is to determine practically and in the concrete the presence or absence of a definite moral obligation, it does not fall within its scope to pass judgment on what would be more advisable, or on what may be recommended as a counsel of perfection. It leaves these judgments to the sciences to which they belong, particularly to pastoral and ascetical theology. The prudent director of consciences, however, being more than a casuist, ought in giving advice to make use of these other sciences in so far as they are applicable. Should he fail to do so, the blame cannot be attributed to casuistry.

The necessity of casuistry and its importance are obvious. From the nature of the case, the general principles of any science in their concrete application give rise to problems which trained and expert minds only can solve. This is especially true regarding the application of moral principles and precepts to individual conduct. For, although those principles and precepts are in themselves generally evident, their application calls for the consideration of many complex factors, both objective and subjective. Only those who unite scientific knowledge of morality with practice in its application may be trusted to solve promptly and safely problems of conscience. Personal, social, commercial, and political experience proves this abundantly. Moral education requires long, patient, and delicate training, and few acquire it without the aid of casuistry. The objections that are urged against casuistry arise from misconception of its purpose and scope, or from errors and abuses that have sometimes accompanied its practice. The former are sufficiently disposed of; the latter no more discredit its legitimate use than the corresponding difficulties which may be raised against therapeutics or civil law impair the value of these sciences. Historically considered, casuistry in some form or other is as old as human conscience. Wherever civilization has developed along moral lines, there the casuist has been for the interior forum of conscience what the judge was for the exterior forum of civil legality. The scope of this article, however, is confined to Catholic casuistry. The history of this may be divided into three periods:

I. FROM THE FIRST TO THE THIRTEENTH CENTURY

During this period, though there are no works treating of casuistry in a formal and scientific way, practical applications of Christian morality to the conduct of life are numerous and continuous; first, in the works of the Fathers and other ecclesiastical writers, in the decisions of popes and bishops, and in the decrees of councils; later, in the Scriptural commentaries, the Books of Sentences, and the Penitential Books.

II. THIRTEENTH TO THE MIDDLE OF THE SIXTEENTH CENTURY

After the Fourth Council of Lateran the reduction to a scientific form of the casuistic doctrine, which had been gradually developed and elaborated during the patristic period, began concurrently with an awakening interest in theological studies and the apostolic activity of the now flourishing mendicant orders. The work of the Dominican, Raymund of Pennafort, entitled "Summa de Poenitentia et Matrimonio", and published about 1235, opened an era in the scientific study of casuistry, and fixed the manner of treatment which the science retained for over two hundred years. Two other books exercised an influence during this period on the formation of scientific casuistry: The "Summa Astesana", published in 1317 by a Franciscan of Asti in Piedmont; and the "Summa Pisana", written by the Dominican Bartholomew of San Concordio, or of Pisa (d. 1347), which treated casuistic subjects alphabetically, and was the first of a long series of similar works. The "Summa Summarum", of Sylvester Prierias, O.P. (d. 1523), practically brings the age of the great "Summists" to a close. St. Antoninus, O.P., of Florence (d. 1459) is notable in his period for his "Summa Confessionalis" and "Summa Confessorum", which were followed by many more manuals of a like kind. He was probably the first who treated moral theology as a distinct science, and thus prepared the way for that closer union of treatment between it and casuistry which finally obtained in the following period.

III. MIDDLE OF THE SIXTEENTH CENTURY TO THE PRESENT TIME

The first hundred years of this period are characterized by a splendid development of theological sciences, due to the ecclesiastical reformation begun and carried out by the Council of Trent, to the institution of a new religious order, the Society of Jesus, and to the intellectual activity evoked in defence of the Church against the pseudo-Reformation of Luther and of contemporaneous heresiarchs. In this progress casuistry shared. Besides the various "Summae Casuum" which were published, the great theologians of the time, in commenting on the second part of the "Summa Theologica" of St. Thomas Aquinas, treated fully and profoundly casuistical questions regarding personal, social, political, and religious duties, regarding the mutual relations of states, and regarding the relative rights of Church and State. During this time moral theology finally attained the dignity of a special science, and became the explicit basis of casuistry. Prominent in bringing about this development were John Azor, S.J. (d. 1603), whose "Institutiones Morales" was printed at Rome in 1600; Paul Laymann, S.J. (d. 1635), who published at Munich in 1625 his "Theologia Moralis"; and Hermann Busembaum (d. 1668), whose "Medulla Theologiae Moralis" became the text for the celebrated commentaries of Claude La Croix, S.J. (d. 1714), of St. Alphonsus Liguori, and in our time of Anthony Ballerini, S.J. The progress of casuistry was interrupted towards the middle of the seventeenth century by the controversy which arose concerning the doctrine of probabilism. This controversy might have been conducted with scientific calm and finally disposed of by the Holy See, but by the injection into it of Jansenistic fanaticism, sophistry, and satire, real issues were confused, and an embittered strife arose, which for nearly two centuries disturbed Catholic schools. The effects on casuistry were deplorable. Two extreme schools, the Rigorists and the Laxists, came into being, and centred attention upon themselves. The vast body of conservative theologians were practically ignored, or charged with laxity because they did not hold the opinions of a narrow school. The Laxists were taken as typical casuists, and because some of them were Jesuits, Jesuit morality became a byword of reproach. The tenets of both Rigorists and Laxists were repeatedly condemned by ecclesiastical authorities; nevertheless the repute of sane casuistry suffered not only among the enemies of the Church, but even to a degree among Catholics also. So much so, that, by the middle of the eighteenth century the very name of casuistry became a synonym for moral laxity -- a signification it yet unfortunately retains in the minds of many whose information on the subject is drawn from prejudiced sources. When Jansenistic rigorism seemed to have attained a permanent triumph, especially in France and Spain, relief was obtained through Alphonsus Maria de Liguori (d. 1787), the saintly founder of the Congregation of the Most Holy Redeemer. By recalling casuists to the study of their classic authors he restored casuistry itself to the place its importance and dignity demanded. His first publication was the "Medulla Theologiae Moralis" of Hermann Busembaum, S.J., with annotations. In eight successive editions this work was enlarged and improved, until it became a synopsis of casuistical literature. The last edition, entitled "Theolgia Moralis", was published in 1785, and received the approbation of the Holy See in 1803. In 1871 Pius IX proclaimed the saintly author a Doctor of the Church. The after-history of casuistry is one of peace and development along the lines laid down by St. Alphonsus.